Generally, the Internet Protocol (IP) and IP networks have been designed to support a single, best-effort class of service. IP networks have successfully transported TCP-mediated data traffic more cost-effectively and flexibly than other popular network types, e.g., circuit-switched networks. As a result, there is a convergence effort to migrate all networked applications, such as voice and videoconferencing applications, to use IP networks as the common transport medium. Best-effort service, however, is not sufficient to meet the Quality-of-Service (QoS) needs of some of these migratory applications, especially in an enterprise environment. Hence, the IP networking industry has been developing QoS solutions with differentiated services that provide different levels of transport performance in accordance with the needs of higher level applications.
A part of many QoS solutions is performance measurement, and specifically the measurement of the current delay, jitter (delay variance), and packet loss probability values for packet traffic traversing communications links connecting routers and switches and traversing multi-hop switched and routed paths through the network. Measured delay, jitter, and packet loss probability values may be used in the decision processes of higher-level functions such as an admission control system, which governs which traffic enters the network.
Admission control is required, for example, to support QoS for many inelastic applications. A number of techniques have been proposed or suggested for admission control in packet-switched networks. For example, U.S. patent application Ser. No. 11/111,464, entitled “Method and Apparatus for Quality-of-Service-Based Admission Control,” incorporated by reference herein, discloses QoS-based admission control (QBAC) techniques for a packet network.
Performance measurement techniques may be categorized as passive, active, or hybrid. Passive techniques measure statistics of actual bearer (non-synthetic) traffic. Active techniques probe the network with synthetic traffic. Hybrid techniques combine passive and active methods to improve accuracy and reduce active traffic loads. Probing a network with test traffic can potentially affect the performance of bearer traffic. Thus, it is important to minimize the complexity of the test architecture, i.e., to use the minimum amount of test traffic necessary to collect the required information.
When it is possible to observe the traffic that enters and exits both ends of an individual link, then measuring the transport performance supported by the link is relatively straightforward. Often, however, geographically distributed enterprises contract with service providers to provide wide-area network (WAN) interconnectivity for connecting their local-area networks (LANs) together to form internetworks. In such cases, the enterprise cannot observe the traffic entering and exiting the access link termination point in the service providers' networks. Because access links are often the bottleneck links in a network and therefore primary contributors to degradation in transport QoS, performance measurements for these access links are critical for QoS management and support of higher-level functions. In this case, naive methods exist to collect the performance measurements needed to support higher level functions, but they generate too much test traffic, i.e., the test traffic volume is large enough to significantly affect the transport performance of application traffic.
A need therefore exists for methods and apparatus for measuring and evaluating access link performance in IP networks that reduce the amount of required test traffic.